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Now that we understand how alpha channels work, let's see how it's used in the actual painting. I am going to zoom in up here to this shadow area up here, the shadow being cast on this wall. Now, if you really study how shadows work, you will notice that as they get further away from the object that's casting the shadow, it starts to soften up. So you see the shadow right here, that it's kind of sharp down here at the edge of the building, and it's getting softer as it gets further back. So let's create that effect right now using an alpha channel. I have here a file in which I've created a couple of layers.
You can see that I have the wall edge, right here-- that's this piece right here--the wall, which is this brown piece here, and a building, this blue area here. And the background just has gradient of grays. We are going to cast a shadow across this wall that's being cast by this blue building. The wall is a little recessed, so there will be a little bit of a shadow cast on the face right here over the wall edge. So right there in front of that layer, I am going to create a layer and call it shadow. In fact, let's make it easier.
I can just use the wall itself, make it a selection, and then in that layer I am going to fill that selection with black. I just did a fill, go in here and say Fill, Foreground Color, OK, and here you can see that it's black. So I am going to deselect it and bring that layer up a little bit so it's just at that edge right there, and it's being cut here, because it's behind the wall right there. And I am going to blur it just a little bit. So I'll go in there and say Gaussian Blur of about, let's say 2 is good right there.
Click OK, bring down the Opacity a little bit to about 70%, put it in Multiply mode, so that we have a nice effect on the colors behind, and then I am going to clip it with that wall edge. So now I am seeing it only inside there. Now the wall on this side has the shadow being cast at an angle based on how far this building is from the wall. So I am going to go in here and I am going to use my Pen tool and right from this edge, right there, I am going to create my first point and then come up here and figure out my angle.
That's going to be about right, just about there. So now I'll just come out here and complete the shape that I want like that. So on top of the layer of the wall right there, I am going to create this, another shadow, shadow2. And I got that path, so I am going to take that path and say fill it with the black, turn off my path, go back to looking at the layers, and we see that there's the effect, which I am going to go ahead and clip it with the wall just like I did with the other shadow.
There it is clipped with the wall. I am going to bring the Opacity down to just 70%, and I am going to put it in Multiply mode, and I am going to give it that same filter of Gaussian Blur just as it was, and there we can see the softening right there. So now as that shadow gets further away, it has to get softer up in this area here. So I have to apply that Gaussian Blur filter a few more times, but I want it to work gradually, not evenly all the way across as the first Gaussian Blur did.
I need to have it to happen gradually, and that's where the alpha channel comes in. So what I am going to do is I am going to go to my Channels and say give me a channel. Now, I want to know exactly where I am placing my effects, so I am going to look at the other channels on top of it. And there I see my wall exposed, so I know that I want to kind of start right about here to soften it all the way up to the top. So if you remember that black protects and white exposes, I am going to get my Gradient tool and right now I have black as my foreground color, so that's going to be the first color.
So I am going to say from right about here right up to there, I create my gradient, and there is the gradient that I am seeing. Now go back over to the RGB and turn this guy off. We can see that the alpha channel had no effect on my image. It is simply a mask through which I will apply those effects. When we look at just the channel itself, there we see that it's a gradient that's going to have no effect here on my image, full effect up here, and a gradual effect through the area of the grays.
So when I come back only here, I make sure I am in the layer of the shadow right there. So now, I am going to load the alpha channel. So I am going to go in there and Command+Click, Ctrl+Click on it, which loads it right there. Now I usually like hide the marching ants, so I can really see the image in full without those distracting animated things going around. So I am just going to say turn off the selection edges. There we go. So now we don't see them. It is still selected, but we just don't see that selection. I am in the layer of the shadows, so I am going to go in there and get my Gaussian Blur filter.
Now I'm going to apply it a few times at a low setting. The reason I am going to do that is if I apply it at a high setting, you notice what's happening? It's softening, but it's still kind of sharp in the middle. So I don't want to do it that way. I want to do it in small increments at a time, so I'm going to apply-- let's try a 5. 5 is good. So I am going to click OK and there you can see it's done the effect. I am going to apply it again. So I will just say apply the filter again and again. You see that it's Command+F, so I am just going to do it by the keyboard, and apply it a few times, and you can see how the shadow is softening as it gets further away.
I am still applying it one more time, and here it comes one more, and there we see the effect that now is still sharp down here, slowly getting softer as it gets further away, and when it gets way up here, it's very soft. So it's giving me a realistic-looking shadow by applying the filter through a selected area based on an alpha channel, which gave me a gradient, which allowed me to apply the effect strongly in one spot and not at all in another.
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